Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications such as angina pectoralis and incontinence. Deep Brain Stimulation (DBS) has also been applied therapeutically for well over a decade for the treatment of refractory chronic pain syndromes, and DBS has also recently been applied in additional areas such as movement disorders and epilepsy. Further, Functional Electrical Stimulation (FES) systems such as the Freehand system by NeuroControl (Cleveland, Ohio) have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients. Furthermore, in recent investigations Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation. Occipital Nerve Stimulation (ONS), in which leads are implanted in the tissue over the occipital nerves, has shown promise as a treatment for various headaches, including migraine headaches, cluster headaches, and cervicogenic headaches.
These implantable neurostimulation systems typically include one or more electrode carrying stimulation leads, which are implanted at the desired stimulation site, and a neurostimulator (e.g., an implantable pulse generator (IPG)) implanted remotely from the stimulation site, but coupled either directly to the stimulation lead(s) or indirectly to the stimulation lead(s) via a lead extension. Thus, electrical pulses can be delivered from the neurostimulator to the stimulation leads to stimulate the tissue and provide the desired efficacious therapy to the patient. The neurostimulation system may further comprise a handheld patient programmer in the form of a remote control (RC) to remotely instruct the neurostimulator to generate electrical stimulation pulses in accordance with selected stimulation parameters. A typical stimulation parameter set may include the electrodes that are acting as anodes or cathodes, as well as the amplitude, duration, and rate of the stimulation pulses.
Thus, the RC can be used to instruct the neurostimulator to generate electrical stimulation pulses in accordance with the selected stimulation parameters. Typically, the stimulation parameters programmed into the neurostimulator can be adjusted by manipulating controls on the RC to modify the electrical stimulation provided by the neurostimulator system to the patient. Thus, in accordance with the stimulation parameters programmed by the external control device, electrical pulses can be delivered from the neurostimulator to the stimulation electrode(s) to stimulate or activate a volume of tissue in accordance with a set of stimulation parameters and provide the desired efficacious therapy to the patient. The best stimulus parameter set will typically be one that delivers stimulation energy to the volume of tissue that must be stimulated in order to provide the therapeutic benefit (e.g., treatment of pain), while minimizing the volume of non-target tissue that is stimulated.
The RC may, itself, be programmed by a clinician, for example, by using a clinician's programmer (CP), which typically includes a general purpose computer, such as a laptop, with a programming software package installed thereon. Typically, the RC can only control the neurostimulator in a limited manner (e.g., by only selecting a program or adjusting the pulse amplitude or pulse width), whereas the CP can be used to control all of the stimulation parameters, including which electrodes are cathodes or anodes.
In the context of an SCS procedure, one or more stimulation leads are introduced through the patient's back into the epidural space, such that the electrodes carried by the leads are arranged in a desired pattern and spacing to create an electrode array. One type of commercially available stimulation leads is a percutaneous lead, which comprises a cylindrical body with ring electrodes, and can be introduced into contact with the affected spinal tissue through a Touhy-like needle, which passes through the skin, between the desired vertebrae, and into the epidural space above the dura layer. After proper placement of the stimulation leads at the target area of the spinal cord, the leads are anchored in place at an exit site to prevent movement of the stimulation leads.
To facilitate the location of the neurostimulator away from the exit point of the stimulation leads, lead extensions are sometimes used. The stimulation leads, or the lead extensions, are then connected to the IPG, which can then be operated to generate electrical pulses that are delivered, through the electrodes, to the targeted tissue, and in particular, the dorsal column and dorsal root fibers within the spinal cord. The stimulation creates the sensation known as paresthesia, which can be characterized as an alternative sensation that replaces the pain signals sensed by the patient. Intra-operatively (i.e., during the surgical procedure), the neurostimulator may be operated to test the effect of stimulation and adjust the parameters of the stimulation for optimal pain relief. The patient may provide verbal feedback regarding the presence of paresthesia over the pain area, and based on this feedback, the lead positions may be adjusted and re-anchored if necessary. A computer program, such as Bionic Navigator®, available from Boston Scientific Neuromodulation Corporation, can be incorporated in a clinician's programmer (CP) (briefly discussed above) to facilitate selection of the stimulation parameters. Any incisions are then closed to fully implant the system. Post-operatively (i.e., after the surgical procedure has been completed), a clinician can adjust the stimulation parameters using the computerized programming system to re-optimize the therapy.
The efficacy of SCS is related to the ability to stimulate the spinal cord tissue corresponding to evoked paresthesia in the region of the body where the patient experiences pain. Thus, the working clinical paradigm is that achievement of an effective result from SCS depends on the neurostimulation lead or leads being placed in a location (both longitudinal, lateral, and depth) relative to the spinal tissue such that the electrical stimulation will induce paresthesia located in approximately the same place in the patient's body as the pain (i.e., the target of treatment). If a lead is not correctly positioned, it is possible that the patient will receive little or no benefit from an implanted SCS system. Thus, correct lead placement can mean the difference between effective and ineffective pain therapy, and as such, precise positioning of the leads proximal to the targets of stimulation is critical to the success of the therapy.
For example, multi-lead configurations, which enable more programming options for optimizing therapy, have been increasingly used in SCS applications. The use of multiple leads that are grouped together in close proximity to each other at one general region of the patient (e.g., side-by-side parallel leads along the spinal cord of the patient), increases the stimulation area and penetration depth (therefore coverage), as well as enables more combinations of anodic and cathodic electrodes for stimulation, such as transverse multipolar (bipolar, tripolar, or quadra-polar) stimulation, in addition to any longitudinal single lead configuration. Furthermore, with these lead configurations, current can be manipulated between leads medio-laterally to create the desired stimulation field. The resulting stimulation field is highly dependent on the relative position of the electrodes selected for stimulation.
Although the lead(s) may initially be correctly positioned relative to each other or relative to the stimulation target(s), the lead(s) are at risk of migration relative to each other and/or relative to the stimulation target(s). The lead(s) may migrate both acutely (e.g., during posture change or during activity/exercise) or chronically. In the context of SCS, the lead(s) may potentially migrate in three dimensions (rostro-caudally (along the spinal cord), medio-laterally (lateral to the spinal cord), and dorsal-ventrally (depth of the lead relative to the spinal cord). Notably, because the thickness of the cerebral spinal fluid (CSF) between the lead(s) and the spinal cord vary along the length spinal cord, migration of the lead(s) in the rostro-caudal direction may necessarily result in dorsal-ventral migration of the lead(s).
As a result, the therapy provided to the patient by the neurostimulation system may be compromised. Once this occurs, the patient may have to schedule another visit to the physician or clinician in order to adjust the stimulation parameters of the system by reprogramming the neurostimulator to compensate for the lead migration. Until the neurostimulator is reprogrammed, however, the patient will not be getting the quality of therapy previously provided by the neurostimulation system. Furthermore, before realizing that a visit to the physician or clinician is necessary, the patient may attempt to improve the compromised therapy by adjusting the stimulation energy delivered by the neurostimulation system via operation of the RC. However, not knowing that the lead migration is the reason for the compromised therapy, and given that the RC only has limited control over the neurostimulator (which typically allows only selection of programs and adjustment of pulse amplitude and pulse width), the patient will not be able to compensate for lead migration, which typically would require a modification in the electrodes that serve as cathodes/anodes—a skill a patient would typically not have.
When lead migration occurs, proper paresthesia coverage can most often be recaptured by reprogramming the IPG, e.g., by using the Bionic Navigator® software. When multiple percutaneous leads are used, programming of the IPG often requires the knowledge of the relative positions between the leads in order to properly place the poles of the generated electrical field. Such information, however, is not readily available to the programmer unless fluoroscopic imaging is performed. Fluoroscopic imaging involves ionized radiation, adds time and cost, and requires a bulky instrument, both of which may limit its use in the clinical setting, and effectively prevent its use outside of the clinical setting. Thus, lead migration continues to be the most common technical complication of spinal cord stimulation therapy. A literature review suggested the incident rate of lead migration was approximately 13.2% (see T. Cameron, Safety and Efficacy of Spinal Cord Stimulation for the Treatment of Chronic Pain: a 20-Year Literature Review, J Neurosurg: Spine 2004, 100: 254-267).
In addition to lead migration, the occurrence of faulty electrodes may also compromise neurostimulation therapy. In particular, in the case where one or more electrodes that have been programmed to deliver the neurostimulation therapy have failed, the resulting stimulation field will change due to the inability of the failed electrode(s) to contribute to the resulting stimulation field. In the same manner described above, with the same problems, the IPG may be reprogrammed to recapture proper paresthesia coverage.
There, thus, remains a technique that better addresses the needs of a user when an implanted stimulation lead has migrated in the patient or an electrode has failed.